From Star Trek
Tholians, Gamilons, Breen, Dominion
From Babylon 5
Pretty much any of the existing factions or subfactions - imagine the PsiCops buying tech off the Ferengi, to use in the Telepath War.
From Elsewhere
Spoilt for choice really:-
Mesa (from the Honorverse) the ship tech would be pretty overwhelming, so tough they shrug off near-miss nukes
Posleen (Legacy of the Alldenata) just for sheer numbers
Voltarian Confederacy (Mission Earth) Jettero Heller must inflitrate the Interstellar Alliance to prevent the rise of a rival power
Necromunger (Chronicles of Riddick) The last Furyan takes refuge on Babylon 5
Zeon (Gundam 0079) The colonies rise against the Earth Alliance, with an army of Mobile Suits
Genom Corporation (Bubblegum Crisis) which would be a bit like the early UF, but still has potential
Kronos (Biobooster Armor Guyver) the Vorlons may have left more than telepathy when they mucked around with the human race's genetics
Kabuto (Tenchi Muyo!) he wants the Great Machine and nothing will get in his way
Steel Angels (Steel Angel Kurumi) several attempts to duplicate Data's technology have been released into an alternate dimension...
D for Drakensis
You're only young once, but immaturity is forever.
Tholians, Gamilons, Breen, Dominion
From Babylon 5
Pretty much any of the existing factions or subfactions - imagine the PsiCops buying tech off the Ferengi, to use in the Telepath War.
From Elsewhere
Spoilt for choice really:-
Mesa (from the Honorverse) the ship tech would be pretty overwhelming, so tough they shrug off near-miss nukes
Posleen (Legacy of the Alldenata) just for sheer numbers
Voltarian Confederacy (Mission Earth) Jettero Heller must inflitrate the Interstellar Alliance to prevent the rise of a rival power
Necromunger (Chronicles of Riddick) The last Furyan takes refuge on Babylon 5
Zeon (Gundam 0079) The colonies rise against the Earth Alliance, with an army of Mobile Suits
Genom Corporation (Bubblegum Crisis) which would be a bit like the early UF, but still has potential
Kronos (Biobooster Armor Guyver) the Vorlons may have left more than telepathy when they mucked around with the human race's genetics
Kabuto (Tenchi Muyo!) he wants the Great Machine and nothing will get in his way
Steel Angels (Steel Angel Kurumi) several attempts to duplicate Data's technology have been released into an alternate dimension...
D for Drakensis
You're only young once, but immaturity is forever.